<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" ref="progressBtn"
            @touchstart.prevent = "progressTouchStart"
            @touchmove.prevent = "progressTouchMove"
            @touchend = "progressTouchEnd">
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>

<script type="text/ecmascript-6">
  import {prefixStyle} from '../../common/js/dom'

  const progressBtnWidth = 16
  const transform = prefixStyle('transform')

  export default {
   props: {
     percent: {
       type: Number,
       default: 0
     }
   },
   created() {
     this.touch = {}
   },
   methods: {
     progressTouchStart(e) {
       this.touch.initiated = true
       this.touch.startX = e.touches[0].pageX
       this.touch.left = this.$refs.progress.clientWidth
     },
     progressTouchMove(e) {
       if(!this.touch.initiated) {
         return 
       }
       const deltaX = e.touches[0].pageX - this.touch.startX
       const offsetWidth = Math.min(this.$refs.progressBar.clientWidth - progressBtnWidth,
       Math.max(0,this.touch.left + deltaX))
       this._offset(offsetWidth)
     },
     progressTouchEnd() {
       this.touch.initiated = false
       this._triggerPercent()
     },
     progressClick(e) {
      //  this._offset(e.offsetX)
       const rect = this.$refs.progressBar.getBoundingClientRect()
       const offsetWidth = e.pageX - rect.left
       this._offset(offsetWidth)
       this._triggerPercent()
     },
     _triggerPercent() {
       const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
       const percent = this.$refs.progress.clientWidth / barWidth
       this.$emit('percentChange',percent)
     },
     _offset(offsetWidth) {
       this.$refs.progress.style.width = `${offsetWidth}px`
       this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`
     }
   },
   watch: {
     percent(newPercent) {
       if(newPercent >= 0 && !this.touch.initiated) {
         const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
         const offsetWidth = newPercent * barWidth
         this._offset(offsetWidth)
       }
     }
   }
  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"

  .progress-bar
    height: 30px
    .bar-inner
      position: relative
      top: 13px
      height: 4px
      background: rgba(0, 0, 0, 0.3)
      .progress
        position: absolute
        height: 100%
        background: $color-theme
      .progress-btn-wrapper
        position: absolute
        left: -8px
        top: -13px
        width: 30px
        height: 30px
        .progress-btn
          position: relative
          top: 7px
          left: 7px
          box-sizing: border-box
          width: 16px
          height: 16px
          border: 3px solid $color-text
          border-radius: 50%
          background: $color-theme
</style>